Engineers propose ‘less is more’ plan to fix Millennium Tower’s sinking, leaning
Prior efforts led to further settlement for San Francisco’s tallest residential building, putting work to address both issues on hold
There’s yet another new plan to right the leaning tower of San Francisco after previous fixes failed.
Engineers are working on a strategy for the Millennium Tower that involves fewer piles than prior efforts, which caused the city’s tallest residential building to sink further into the ground.
The plan involves installing 18 piles to reduce weight from the 58-story structure’s foundation, the San Francisco Chronicle reported this week. The project’s engineering and construction teams initially aimed to install 52 piles to anchor it to a level of bedrock 250 feet below the ground. Yet they put that work on hold after it sank another inch while they tested pile installation this summer, causing them to go back to the drawing board.
Project engineers believe the new plan will mitigate Millennium Tower’s sinking and leaning, alleviate stress on its existing foundation and decrease construction times, lead project engineer Ronald Hamburger of Simpson Gumpertz & Heger wrote Tuesday in a letter to the city and Millennium Tower’s homeowners obtained by the Chronicle. Stress tests they conducted showed that the piles can handle more weight than previously projected, so they want to increase each column’s weight load 25 percent to 1 million pounds, the Chronicle reported.
The proposal falls within the $100 million budget of the original plan, which is funded by a confidential agreement in 2018 that compensated the tower’s condominium owners for value lost due to its construction issues. The latest fix is expected to be completed by the end of next year, assuming the city gives it the OK. The San Francisco Municipal Transportation Authority board has already approved it, and the project’s engineering team plan to apply for an updated building permit, the Chronicle reported.
Completed in 2009 and located at the corner of Mission and Fremont streets, the 419-unit Millennium Tower is the most expensive residential project in San Francisco’s history. Since opening that year, it’s sunk about 18 inches and tilted 22.5 inches to the west and nine inches to the north, sparking a class-action lawsuit between its residents and Millennium Partners, the building’s developer, that the parties settled in 2018.
Since work to secure the building’s north and west sides began in May, the tower has settled almost two inches at its northwest corner and tilts a little more than two feet at the same edge, NBC Bay Area reported earlier this month. Around that time, Hamburger assured city officials that the settlement that’s occurred while he and his project team tested piles was within expected levels, and that they needed to conduct more tests to determine the exact number of piles needed to shore up the building’s foundation.
[San Francisco Chronicle] — Matthew Niksa